JPH0371439A - Method and device for tracking servo in optical disk device - Google Patents

Abstract

PURPOSE:To perform tracking servo based on an accurate error signal obtained with a detecting means for a tracking error signal by selecting the detecting means for the optimum tracking error signal corresponding to recording or reproduction, respectively. CONSTITUTION:A sensor 5 as a first detecting means using a multipartite sensor part as a sensor part 4 and which detects and outputs a tracking error signal by a push-pull method, sensors 6 and 7 as second detecting means which detect and output the tracking error signal by a three-beam method are arranged at prescribed positions. The tracking servo is performed by inputting the output of a terminal 10 that is the output of the first detecting means 5 to a servo circuit when the recording is performed. Also, the tracking servo of a pickup is performed by inputting the output of a terminal 11 that is the output of the second detecting means 6 and 7 to the servo circuit when the reproduction is performed. In such a way, the accurate error signal can be obtained when the recording or the reproduction is performed, and the accurate tracking control of the pickup can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a pickup tracking servo method in an optical disc recording/reproducing apparatus and an optical disc device using the servo method.

(b) Prior Art In the servo system of the pickup of an optical disc device, typical methods for detecting tracking error signals include the three-beam method and the push-pull method.

The three-beam method is stable against eccentricity of the optical disc, etc.
It is used in compact discs, optical bidet discs, etc., and the push-pull method is used in data file devices, etc.

By the way, in conventional optical disc devices, only one type of error signal detection method is used in one tracking servo system.

On the other hand, for example, Nikkei Electronics January 2, 1989
As described in the article ``A write-once optical disk that satisfies the rCD standard, recording by thermal deformation of the interface between the substrate and the dye layer'' on page 107 of the 3rd issue, in a recordable optical disk, tracking is performed before and after recording. There are disks in which the shape of the guide groove changes.

When using the above-mentioned optical disc as a recording medium and considering compatibility with current compact discs, during playback,
Preferably, the three-beam method used by current compact disc players is used. This is because the movement of the objective lens of the pickup by the tracking servo does not cause the occurrence of DCC offset of the tracking error signal, and is stable against eccentricity of the disk.

(c) Problems to be Solved by the Invention However, when the three-beam method is used in the tracking servo system for the above-mentioned recordable optical disc, there are the following problems.

FIG. 4 is a characteristic diagram comparing the degree of modulation of the cross-track signal before and after recording on the above-mentioned optical disc. As shown in FIG. 4, while the modulation degree before recording is 10%, there is a large difference of 25% after recording.

Moreover, FIG. 5 is a schematic diagram showing the optical disc surface during recording by the three-beam method.

In the push-pull method, sub-beams (13) and (14) are placed before and after a main beam (12) for recording. The reflected lights of the two sub-beams (13) and (14) from the optical disk are detected by separate sensors, and a tracking error signal is obtained from the difference.

As described above, when tracking servo is performed on an unrecorded portion, as shown in FIG. 4, the degree of modulation of the signal is small, so it is not possible to obtain a sufficient tracking error signal.

Furthermore, in the case of tracking servo during recording, for example, as shown in FIG.
is the part after recording.

The signals obtained by the two sub-beams (13) and (14) have different degrees of modulation, as shown in Figure 4, and the error signal obtained as the difference between them has a DC component, so it is not accurate. No.

The present invention has been made to solve the above-mentioned problems, and provides a method for obtaining accurate tracking error signals and performing tracking servo both during recording and reproduction, and an optical disc device using the method. The task is to

(d) Means for Solving the Problems The tracking servo method according to the present invention includes a first detection means that detects and outputs a tracking error signal of the pickup by a push-pull method, and a first detection means that detects and outputs a tracking error signal of the pickup using a push-pull method. and a second detection means that detects and outputs by a beam method, selects the first or second detection means according to the operation mode of the optical disk device, and based on the error signal from the selected detection means, It is characterized by performing pickup tracking servo.

Further, the optical disk device according to the present invention includes a pickup that irradiates a beam from one light emitting means to write information on the optical disk or reads information written on the optical disk using reflected light from the optical disk, and a pickup that outputs a tracking error signal of the pickup. a first detection means that detects and outputs the signal using the buoyble method; a second detection means that detects and outputs a tracking error signal of the pickup using the three-beam method; and an output of the first or second detection means. a servo circuit that performs tracking servo of the pickup according to the recording or reproducing operation;
and a switching circuit for switching the output of the detection means to the servo circuit.

(E) Function According to the method of the present invention, depending on the operation mode of the optical disc device, the first detecting means is used in the case of recording, and the second detecting means is used in the case of reproducing. By selecting the detection means, accurate error signals can be obtained and stable tracking servo can be performed.

(f) Examples Examples of the present invention will now be described with reference to the drawings.

FIG. 1 is a schematic diagram showing a pickup section used in the present invention, and FIG. 2 is a circuit diagram showing a sensor section for detecting a tracking error signal and a preamplifier diagram.

In these figures, (1) is a light emitting means such as a laser diode, and the beam emitted from this light emitting means (1) is separated into three beams, a main beam and two sub beams, by a diffraction grating (2). and irradiates the optical disc (3).

(4) is a tracking sensor section consisting of a photodetector that detects the reflected light of the optical disk irradiated with the beam.

This sensor section (4) is multi-divided, with a sensor (5) serving as a first detection means that detects and outputs a tracking error signal using a push-pull method, and a sensor (5) that detects and outputs a tracking error signal using a three-beam method. Sensors (6) and (7) serving as second detection means for detecting and outputting are arranged at predetermined positions.

The output from the sensor (5) is input to a differential amplifier (8), and a tracking error signal detected by the push-pull method is output from the differential amplifier (8) from a terminal (10).

On the other hand, the output from the sensors (6) and (7) is the differential amplifier (9).
), and a tracking error signal detected by the push-pull method from the differential amplifier is output from a terminal (11).

Now, in the tracking servo method according to the present invention, the detection output of the above-mentioned first or second detection means is selected depending on the operation mode of the optical disc device. That is, during recording, the output of the terminal (10), which is the output of the first detection means, is input to the servo circuit to perform tracking servo.

During playback, the output from the terminal (11), which is the output of the second detection means, is input to the servo circuit to perform tracking servo of the pickup.

According to the method of the present invention, during recording or reproduction,
Accurate error signals can be obtained and accurate tracking control of the pickup can be performed.

FIG. 3 is a block diagram showing the configuration of an optical disc device according to the present invention.

In FIG. 3, (31) is a pickup section, which includes a light emitting means (1), a diffraction grating (2), a sensor (4), etc. as shown in FIG. (32) is a preamplifier, which outputs a tracking error signal using the push-pull method as the first detection means to the terminal (10), as shown in FIG. A tracking error signal based on the method is output to a terminal (11).

(33) is a switching circuit, which switches the output of the error signal derived to the servo circuit (34) to the terminal (lO) or the terminal (11) according to the output of the setting circuit (35) that sets the recording/playback operation mode. . That is, when the operation mode is set to recording, the operation mode setting circuit (35) changes to the switching circuit (
33) switches to the output terminal (10) side of the first detection means using the push-pull method.

On the other hand, when the operation mode is set to reproduction, the operation mode setting circuit (33) switches to the output terminal (11) of the second detection means using the three-beam method.

Then, the servo circuit (34) performs tracking servo of the pickup (31) based on the error signal output from the first or second detection means suitable for recording or reproduction, respectively.

(G) As described in detail, according to the present invention, it is possible to select the optimal tracking error signal detection means for recording or reproduction, so that accurate error signals obtained from this detection means can be obtained. Based on this, tracking servo can be performed and tracking servo performance is improved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the pickup section used in the present invention, FIG. 2 is a circuit diagram showing the sensor section and preamplifier section for detecting the tracking error signal of the present invention, and FIG. 3 is an implementation of the device of the present invention. FIG. 2 is a block diagram illustrating an example. FIG. 4 is a characteristic diagram comparing the degree of modulation of the cross-track signal before and after recording, and FIG. 5 is a schematic diagram showing an optical disc during recording by the 3-beam method. l... Light emitting means, 2... Diffraction grating, 3... Optical disk, 4.5.6.7... Sensor, 8.9... Differential amplifier, 10... First detection Output terminal by means, 1
DESCRIPTION OF SYMBOLS 1... Output terminal by the second detection means, 31... Pick-up section, 32... Preamplifier section, 33... Switching circuit, 34... Servo circuit, 35... Operation setting circuit.

Claims (2)

[Claims] (1) A first detection means that detects and outputs a tracking error signal of the pickup using a push-pull method, and a second detection means that detects and outputs a tracking error signal of the pickup using a three-beam method. A tracking servo for an optical disc device, characterized in that the first or second detection means is selected depending on the operating mode of the optical disc device, and the tracking servo of the pickup is performed based on the error signal from the selected detection means. Method. (2) A pickup that irradiates a beam from a light emitting means to write information on an optical disk or reads information written on an optical disk using reflected light from the optical disk, and detects a tracking error signal of the pickup using a push-pull method. a first detecting means for outputting a tracking error signal; a second detecting means for detecting and outputting a tracking error signal of the pickup by a three-beam method;
a servo circuit that performs tracking servo of the pickup according to the output of the detection means; and a switching circuit that switches the output of the first or second detection means to the servo circuit based on a recording or reproduction operation. An optical disc device.